A study tailor-made for Cosmo has found that when ladies shower their pets with love, they want their boyfriends to do the same (to the pets, that is). If they have a cooler relationship with their cat or dog or miniature chameleon (although how you could have a cool relationship with a miniature chameleon is beyond me), they also want dudes to act cool towards said pet. Otherwise, they get jealous. A dude, however, is apparently less likely to care how his lady-friend treats his pet. Study author Kristen Capuozzo explains her results thus:

Females are much more in-tune with the harmony of the household. Is everybody getting along? Is there any kind of disagreement, any discord? If I'm super-attached to my pet and my husband isn't, then that might cause some disharmony: 'Why is that pet in my bed? Why are you spending so much money on that pet?'

Just to be safe, though, you should probably be nice to your significant other's pet, because people who are mean to pets are assholes.